Unsaturated monomers, particularly olefin monomers, are polymerized in a variety of polymerization processes using a wide variety of catalysts and catalyst systems. One of the most common polymerization process used in the production of olefin based polymers such as polyethylene or polypropylene (homopolymers as well as copolymers), is a solution based process. In such a process the formed polymer is dissolved in the polymerization medium. Often, the catalyst and monomer are also dissolved in the polymerization medium, but that is not a requirement of a “solution” process. In typical solution processes, the polymerization temperature may be at, above or below the melting point of the dry polymer. For example, in typical solution phase polyethylene processes, polymerization takes place in a hydrocarbon solvent at temperatures above the melting point of the polymer and the polymer is typically recovered by vaporization of the solvent and any unreacted monomer. In some cases solvents or diluents are used, while in others the monomer to be polymerized also acts as the solvent (e.g. a bulk process). In each of these “solution” systems, there remain factors that influence not only the rate and volume at which the polymerization can run, but can also influence the properties of polymer produced.
In a typical solution process, the polymer formed is dissolved in the solvent. The higher the concentration of the polymer, the higher the viscosity of the polymerization reaction mixture containing polymer, monomers and solvent. The polymer concentration is limited by viscosity for easy handling and process economics. This is especially true for polymers with high molecular weight.
An alternative to a solution process is the slurry process in which the polymer product forms a slurry rather than a solution in the polymerization medium. Viscosity in a slurry reactor, is lower due to the formation of polymer particles in the reaction medium. In such situations, the viscosity of the polymer slurry does not increases as rapidly as the polymer concentration increases and therefore polymer concentration (or loading) can be increased up to 40% as compared with less than 20% in solution process. Slurry processes also facilitate the production of high molecular weight polymers (>100 Mooney viscosity) due to the nature of low viscosity as compared to that in solution reactors. Moreover, there is less solvent to remove and the quantity of recycled solvent is reduced considerably in a slurry process.
Polymers with low crystallinity or low melting temperature are often produced in a solution process due to the selected operating windows optimized for catalyst and process economics. In the course of finishing, unreacted monomers and solvent are progressively removed from the polymerization mixture until polymer can form solid pellets or bales.
Generally polymer solutions can undergo phase separation at the lower critical solution temperature. The phase separation is encouraged by higher temperature and/or lower pressure. Appropriate selection of polymerization solvent, monomer conversion, especially of the volatile monomers, temperatures, and pressures is required to avoid phase separation. Solvents such as hexane may require an elevated operating pressure of above 50 bar (5000 kPa) to avoid unwanted phase separation. In solution plants, solvent selection and operating conditions must be designed for a particular operating windows for the desired polymerization process. This operating windows might not be permitted by or optimized for a given polymer type and catalyst. Thus there is a need in the art for an improved process which can produce such polymers in a slurry form.
Many polymers are insoluble in the reaction mixture from which they are formed. Upon significant polymerization, polymer chains reach a crystallizable length and polymer nucleation and crystallization begin. The crystallization of polymers leads to polymer-solvent phase separation. On the other hand, polymer-solvent phase separation can be also induced through change of solvency of the reaction medium with respect to the polymer produced. The instant invention provides a process that with proper selection of a fluorinated hydrocarbon or a mixture of fluorinated hydrocarbons and hydrocarbon solvents, the process can be operated in a slurry mode instead of solution. Polymers produced will be in solid-state. Thus the process can produce polymers with a wide range of crystallinity or amorphous content.
The instant invention also provides a polymerization method that can produce softer polymers (such as ethylene propylene copolymers and terpolymers) that does not require a dusting agent in the reaction medium, unlike some gas-phase process which require partitioning agent such as talc or carbon black. Likewise, the instant invention also provides a method to prepare ethylene propylene copolymers and terpolymers in granular form (as opposed to crumb/bale form).
U.S. Pat. No. 3,470,143 discloses a process to produce a boiling-xylene soluble polymer in a slurry using certain fluorinated organic carbon compounds.
U.S. Pat. No. 5,990,251 discloses a gas phase process using a Ziegler-Natta catalyst system modified with a halogenated hydrocarbon, such as chloroform.
EP 0 459 320 A2 discloses polymerization in polar aprotic solvents, such as halogenated hydrocarbons.
U.S. Pat. No. 5,780,565 discloses dispersion polymerizations of polar monomers under super-atmospheric conditions such that the fluid is a liquid or supercritical fluid, the fluid being carbon dioxide, a hydrofluorocarbon, a perfluorocarbon or a mixture thereof.
U.S. Pat. No. 5,624,878 discloses the polymerization using “constrained geometry metal complexes” of titanium and zirconium.
U.S. Pat. Nos. 2,534,698, 2,644,809 and 2,548,415 disclose preparation of butyl rubber type elastomers in fluorinated solvents.
U.S. Pat. No. 6,534,613 discloses use of hydrofluorocarbons as catalyst modifiers.
U.S. Pat. No. 4,950,724 disclose the polymerization of vinyl aromatic monomers in suspension polymerization using fluorinated aliphatic organic compounds.
WO 02/34794 discloses free radical polymerizations in certain hydrofluorocarbons.
WO 02/04120 discloses a fluorous bi-phasic systems.
WO 02/059161 discloses polymerization of isobutylene using fluorinated co-initiators.
EP 1 323 746 shows loading of biscyclopentadienyl catalyst onto a silica support in perfluorooctane and thereafter the prepolymerization of ethylene at room temperature.
U.S. Pat. No. 3,056,771 discloses polymerization of ethylene usingTiCl4/(Et)3A1 in a mixture of heptane and perfluoromethylcyclohexane, presumably at room temperature.
Additional references of interest include:
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